This invention relates to a device for introducing additional air into an intake passage leading to a combustion chamber of an internal combustion engine and, more particularly, to an improvement of a device according to U.S. Pat. No. 4,089,312 issued to the present inventor.
During subsequent research and development of the device according to U.S. Pat. No. 4,089,312, it could be noted by the inventor that the advantages of the device are remarkable especially when the pressure in the intake passage is relatively low and that the amount of air introduced into the intake passage becomes a relatively large volume and almost constant below a certain level of vacuum in the intake passage.
According to the analyses of the present inventor of such effects, it could be assumed that when the pressure in the intake passage lowers to a certain level, the flow speed of additional air entering into the intake passage through very small peripheral openings or orifices in an intake manifold reaches a sonic speed. As is known, when the speed of air reaches the speed of sound, a so-called sonic barrier is formed to restrict any further increase of the speed of the air. Due to such sonic condition of the air flow, the flow speed of the additional air to be introduced into the intake passage is restricted from being further increased even when the pressure in the intake passage is decreased below the above certain level. The sonic condition of the air flow causes a microturbulence in the entering into the intake passage from the peripheral openings. The microturbulence in the air is generated only at the periphery of the intake passage defined by the peripheral openings but is activated so much that the fuel in the liquid state not vaporized and flowing down along the periphery of the intake passage is intimately mixed with the additional air entering from the peripheral openings of the intake passage and is effectively vaporized. The fuel mixed with the additional air and vaporized thereby is then led into combustion chambers for better combustion.
The remarkable advantages of the additional air flow could be noticed when the additional air flow reached the sonic condition due to a relatively low pressure in the intake passage, such as at times of engine idling and low speed driving of the engine. At the time when the pressure in the intake passage goes up beyond the above certain level due to relatively high speed driving of the engine, the sonic condition of the additional air flow is lost so that the amount of additional air flowing into the intake passage is decreased and also that the advantages of the microturbulence of the additional air are eliminated.